Carbon isotope analysis and 454 pyrosequencing methods were used to investigate in situ biodegradation of chlorpyrifos during its transport through three model integrated recirculating constructed wetlands (IRCWs). Results show that plant and Fe-impregnated biochar promoted degradation of chlorpyrifos and its metabolite 3,5,6-trichloro-2-pyridinol (TCP). Carbon isotope ratios in the IRCWs shifted to -31.24 +/- 0.58% (IRCW1, plant free), -26.82 +/- 0.60% (IRCW2, with plant) and -24.76 +/- 0.94% (IRCW3, with plant and Fe-biochar). The enrichment factors (.bulk, c) were determined as -0.69 +/- 0.06% (IRCW1), -0.91 +/- 0.07% (IRCW2) and -1.03 +/- 0.09% (IRCW3). Microbial community analysis showed that IRCW3 was dominated by members of Bacillus, which can utilize and degrade chlorpyrifos. These results reveal that plant and Fe-biochar can induce carbon isotope fractionation and have a positive impact on the chlorpyrifos degradation efficiency by influencing the development of beneficial microbial communities. (C) 2017 Published by Elsevier Ltd.